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high-voltage transformer

Started by Winfield Hill October 31, 2019
On 2019-10-31 11:48, Winfield Hill wrote:
> John Larkin wrote... >> >> On 31 Oct 2019 10:08:49 -0700, Winfield Hill <winfieldhill@yahoo.com> >> wrote: >> >>> bloggs.fredbloggs.fred@gmail.com wrote... >>>> >>>> On October 31, 2019, Winfield Hill wrote: >>>>> >>>>> My 1:1 high-voltage transformer is coming along well. >>>>> This is to make 5V, 12V, or whatever at high voltages. >>>>> I'll be using it at 6kV, but it's passing tests at 9kV, >>>>> and I'll do a weekend at 11kV before pronouncing it OK. >>>>> >>>>> The transformer is a small 50-cent common-mode choke, >>>>> TAIYO YUDEN p/n TLF9UA102W0R8K1, footprint only 11x17mm. >>>>> The pins are spaced 8mm. We potted it with vacuum air >>>>> removal, Dow Corning Sylgard-184, otherwise called PDMS. >>>>> Testing with +5kV and -4kV, to avoid corona discharge. >>>>> >>>>> https://www.dropbox.com/s/xtuzkei0xg8huhg/TLF9UA_potted.jpg?dl=1 >>>> >>>> Isn't that wire insulation only good for 4kV? I guess >>>> 11kV isn't enough to cause breakdown between windings. >>> >>> The primary is near ground, and the secondary at HV. >>> The coil voltages are low. I'm relying on the plastic >>> bobbin for winding insulation from the ferrite core. >>> The Sylgard protects all the other paths. The PCB will >>> have a slot between coil sections, and it'll get a coat >>> of urethane. >> >> Test it to breakdown! > > I was worried about the 8mm pin-to-pin clearance, and the > inadequate hardening of my setup, compared to the end-use > installation. I added teflon sleeves to the exposed pins. > > Then I started increasing the voltage towards 11kV. But it > snapped anyway, at 10kV. Everything is still fine, zero uA > leakage, but I'm going to finish with a four day soak test > at 8.5kV, to convince myself it'll be fine for use at 6kV. > > The scheme should be good to higher voltages, with a choke > having more pin clearance, like my original part's 12mm. >
If by "snapped" you mean it started arcing then it is definitely not suitable for 6kV working voltage. There is a huge difference between working voltage and max dielectric withstand. Easily one order of magnitude. Damage introduced by HV testing (such as hipot) is cumulative which is why we are time-limited in medical for such tests. If I needed a LV supply up on a HV rail I'd look at series resonant structured with a massive isolation barrier. Simular to how electric toothbrushes such as Philips Sonicare are charged. -- Regards, Joerg http://www.analogconsultants.com/
Joerg wrote...
> > If by "snapped" you mean it started arcing ...
The arc was external to the transformer, across the thin exposed pins, acting as sharp points. I can harden them in the final product.
> If I needed a LV supply up on a HV rail I'd look at > series resonant structured with a massive isolation > barrier.
I made a serious HV transformer, similar to a TV flyback, and used it at 20kV, but I'm looking for a more simple approach. I think it'll work out OK. -- Thanks, - Win
On 2019-10-31 15:01, Winfield Hill wrote:
> Joerg wrote... >> >> If by "snapped" you mean it started arcing ... > > The arc was external to the transformer, across > the thin exposed pins, acting as sharp points. > I can harden them in the final product. > >> If I needed a LV supply up on a HV rail I'd look at >> series resonant structured with a massive isolation >> barrier. > > I made a serious HV transformer, similar to a TV > flyback, and used it at 20kV, but I'm looking for > a more simple approach. I think it'll work out OK. >
Just be careful. Sometimes HV stuff will initially work, for a while. Then the barrier gradually breaks down until there is a loud bang. Or you arrive at your lab and wonder why there are three fire trucks :-) -- Regards, Joerg http://www.analogconsultants.com/